IGCSE Biology Paper-4: Specimen Questions with Answers 134 - 136 of 279


A biologist performed an experiment to find the optimum pH for the activity of pepsin.

The enzyme activity was measured in four test-tubes. Each test-tube contained a cube of cooked egg white which contains protein.

Fig. shows the four test-tubes.

Solution of Enzyme

The biologist measured the time taken for the complete digestion of the cubes of cooked egg white.

Question 134 (1 of 2 Based on Passage)


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One Liner▾

Temperature must be controlled in this experiment.

Describe how temperature could be controlled.


Using water bath to regulate temperature.

  • Using incubator
  • Solutions must be equilibrated at a specific temperature

  • Using thermometer to check temperature

Question 135 (2 of 2 Based on Passage)


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The biologist ensured all the cubes of cooked egg white were the same size.

Suggest why.


To provide equal surface area for enzymatic activity, it also allows comparison of product with proper experimental validation.

Question 136


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Short Answer▾

Products of digestion are absorbed through the villi in the small intestine.

Explain how villi are adapted for absorption.


Absorption from the small intestine: The small intestine is the main absorptive organ. About 90% of the ingested foodstuffs is absorbed during passage through the small intestine. The surface area of the intestine through which absorption can take place is vastly increased by the circular folds (plicae semilunares) of the mucous membrane and by the large number of villi.

It includes:

  • Absorption of carbohydrates: The products of carbohydrate digestion is absorbed from the intestine into blood of the portal venous system in the form of monosaccharides, chiefly the hexoses (glucose, fructose, mannose, and galactose) .
  • Absorption of amino acids and protein: It is probable that under normal circumstances the dietary proteins are almost completely digested to their constituent amino acids and that these end products of protein digestion are then actively transported from the intestine into the portal blood.

  • Absorption of fats: The dietary fat is digested, by the action of the pancreatic lipase present in the intestine, partially into glycerol and fatty acids and partially to split products such as monoacyl glycerols.

  • Absorption of vitamins: Water-soluble vitamins like members of B complex (except B12) and vitamin C readily diffuse across the walls of the intestine into the blood.